1. Field of the Invention
The present invention relates to display devices, and more particularly, to an integrated black matrix or color filter structure for thin-film transistor (TFT) liquid crystal display (LCD).
2. Description of the Prior Art
The technology of liquid crystal display (LCD)has been continuously developed for several decades to enhance the image displaying quality of various kind of displaying systems. In comparing with conventional cathode radiation tube (CRT) systems, the liquid display system has the advantages such as reduced volume, light weight, low power consumption, and high resolution. Having the application of thin film transistors (TFT) in driving the display cells of the liquid crystal display and accompanying fabrication processes, the size of the display system is further scaled down with the integrated structure design and improved packing density of the semiconductor fabrication technology. The thin film transistor liquid crystal display have been employed in various kind of computer, communication, and consumer electric products such as desktop and notebook computers, personal digital assistant (PDA) devices, mobile communicators and web site browsers, and liquid crystal projectors.
In the design of thin film transistor liquid crystal display, since the thin film transistors and liquid crystal display regions are formed around each other between two light-transparent plates to make the image visible, the circuit and transistor regions which are mostly consisted of non-transparent materials must be shield from being visible, in order the make the image information be displayed with clarity and minimum disturbances from the pattern of non-transparent regions.
FIG. 1 illustrates schematic cross-sectional view of a prior art liquid crystal display device employing thin film transistors. A plurality of thin-film transistors 12 are formed on the bottom plate 10, and the thin-film transistors 12 are provided with source regions S and drain regions D. Pixel element electrodes 14a is formed on the bottom plate 10 to connected with the drain regions D. A common electrode 14b is provided in opposite to the pixel element electrodes 14a with a liquid crystal material 16 therebetween to form a vertical driving display device.
For shielding circuitry and less active display regions, and allow the back light to pass through main display cell regions, a shielding layer, or namely a black matrix or a dark matrix, is provided with a designed pattern corresponding to the regions such as transistors in the figure. In the application of color liquid crystal display device, color filters like red (R), green (G), and blue (B) filters are utilized and placed between the regions of black matrix to create image information in color. Polarizing plates 10a and 20a can also be added respectively outside the bottom plate 10 and a top plate 20.
In the typical design and accompanying fabrication processes of the aforementioned liquid display device, the black matrix 18, the color filters R, G and B, and the common electrode 14b are formed on the top plate 20. The top plate 20 with the layers and patterns formed and the bottom plate 10 with circuitry and transistors are then bonded together with a space provided therebetween for receiving the liquid crystal material 16.
However, having the decreasing scale of liquid crystal display cells in the present stage technology, the size of each display cell can be as small as 23 micrometersxc3x9769 micrometers, or even smaller, which makes the bonding process for the top plate 20 the bottom plate 10 hard to control. The process window for the fabrication process is too small to be followed with high accuracy, the minor shift in aligning the two plates 10 and 20 may lead to the reduction of aperture ratio, which is an index for measuring the relative area of visible transparent regions to the total area, as high as 30% and greatly damage the displaying characteristic and capability of the liquid display device.
Several approaches have been proposed for solving the aforementioned issues. One approach is to extend the region of black matrix 18, like the additional region dX indicated in FIG. 1, thereby providing a increased process window for aligning and bonding the two plates 10 and 20. However, the approach does not solve the problem of decreased aperture ratio, and even make it worse, since the visible area is further reduced by extending the black matrix pattern. Another approach is to form the black matrix pattern directly on the bottom plate, at somewhere between the thin film transistors 12 and the bottom plates. However, the method is only workable for backside illuminated display device and can not be employed for direct viewing display device, under the lack of light shield when being observed from the top side of the display device.
In the design of thin film transistor liquid display device, the capacitive coupling effect of each display cell is important for maintaining the display status, namely the orientation of the liquid crystal molecules. The capacitive coupling effect and the display status of each display cell must be maintained without observable degradation between each scanning cycle, and also for avoiding the influence of undesired leakage and coupling noises. However, having the down-scaling in the size of the display units, the capacitive coupling effect is further limited under limited area. The fabrication of the densely packed display device can be limited without the improvement in providing raised capacitive coupling effect of unit cell in the limited area.
In accordance with the present invention, an active cell for a thin-film transistor liquid crystal display, with integrated black matrix/color filter, is provided. The active cell on a substrate includes a switching device, a data line, a scanning line, a planarization layer, a light shielding layer, a dielectric layer, a first electrode layer, a liquid crystal layer, a second electrode layer, and a counter plate. The switching device is formed on the substrate, wherein the data line supplies data signals to the switching device and the scanning line supplies controlling signals to the switching device. The planarization layer is formed on the switching device and has a contact opening which is extended down to a driven end of the switching device. The light shielding layer is on a portion of the planarization layer and the dielectric layer is on the light shielding layer and a top planar region of the planarization layer. The first electrode layer is formed on the dielectric layer and the planarization layer, and the first electrode layer also communicates to the driven end of the switching device through the contact opening. The liquid crystal layer is on the substrate, the second electrode layer is on the liquid crystal layer, and the counter plate on the second electrode layer.
In the preferred embodiments, the active cell further includes a bias generator which is electrically coupled between the light shielding layer of a conductive material and the second electrode layer, in order to provide a bias voltage between the light shielding layer and the second electrode layer.